BUENOS AIRES -- President Carlos Menem began paying what he called ``a debt to humanity`` on Monday by ordering the release of police files on Nazi war criminals who fled to Argentina after World War II.

Officials said the documents examined thus far chart the lengthy, comfortable stay of Josef Mengele, known as the ``angel of death`` for experiments he performed on inmates of concentration camps. The files also document the uneventful life and times in Argentina of Josef Schwammberger, now on trial in Germany for charges of having slaughtered thousands of Jews in a Polish ghetto.

A file on Martin Bormann, one of Adolph Hitler`s top aides, contains no proof that he ever spent time in Argentina, officials said. Most experts say Bormann died in Germany in 1945, but there have been numerous supposed sightings in various South American countries over the years.

Release of the 10-inch stack of yellowing papers in dog-eared folders represents what Menem characterized as an ``immense`` change in Argentine policy.

Argentina pursued a stubborn, and lucrative, neutrality throughout the war, joining the side of the Allies in the final days when advancing Russian troops were shelling the suburbs of Berlin and Hitler had taken to his underground bunker.

After the war, strongman Juan Peron allowed Nazis to enter the country. The number is disputed, from hundreds to thousands. He and subsequent presidents turned a deaf ear to international authorities trying to hunt down war criminals such as Adolph Eichmann, an architect of the Holocaust. Eichmann lived in a Buenos Aires suburb until 1960, when Israeli commandos kidnapped him and smuggled him to Jerusalem to be tried and hung.

It has fallen to Menem, a Peronist who often proclaims reverence for the Argentine dictator, to undo much of Peron`s legacy. Over the last two years he has dismantled much of the economic structure Peron left behind. Now he is opening to scrutiny Peron`s attitude toward the fleeing Nazis, which seems to have amounted to indifference, if not benign neglect.

Shimon Samuels, director for Europe and Latin America of the Simon Wiesenthal Center, said Menem`s action offered ``a good signal`` that the Argentine government is willing to break with its past.

Samuels said documents in the possession of Argentine authorities might shed light on roles that the Red Cross, the Vatican and other third parties could have played in Nazi escapes after the war, and might offer clues to the whereabouts of loot that war criminals are said to have stashed away.

Menem said he made the decision to open the files during his trip to the United States last November. The issue was raised by representatives of the World Jewish Congress, as well as in articles in the U.S.

Menem`s decree immediately releases federal police files on the Nazis to the Argentine national archives. It gives other government agencies 30 days to search for any additional pertinent documents.